X-Message-Number: 4741 From: Ralph Merkle <> Subject: SCI.CRYONICS Re: Cold Start Date: Tue, 8 Aug 1995 11:58:51 PDT I've received several e-mail messages pointing out various deficiencies in the "Cold Start" scenario (originally published in Cryonics in 1990). These may be summarized as: 1) HF is highly reactive. One issue, the appropriate design of a containing vessel, is merely technical. One need merely look up in an appropriate reference manual the recommended material(s) for a container which holds HF. One reference suggests the use of steel cylinders. I would expect that the fluorinated diamond (111) surface would also be suitably unreactive (similar to Teflon, a polymer of C2F4 monomeric units). The second issue, of much greater concern, is the aesthetics (or lack thereof...) of HF. These were excellently expressed by Charles Platt. The best solution to this problem is to adopt a reaction which is generally accepted to be benign, such as the burning of hydrogen and oxygen to produce water. I did not propose this reaction as it requires either high temperature or a suitable catalyst. I did not have a ready reference available for a catalyst that would work reliably at the required temperature, nor had I verified that a pellet on the order of 0.1 microns in diameter surrounded by tissue at ~140 Kelvins could be heated to the ignition temperature of the 2H2 + O2 reaction and maintained at that temperature despite the flow of heat out of the pellet. Perhaps someone would be kind enough to propose an ignition mechanism and perform the necessary thermal calculations. H2 + F2 is a reaction that proceeds spontaneously at any temperature down to (if memory serves) 20 Kelvins. 2) The temperature immediately surrounding the heating pellets might cook the surrounding tissue. This can be addressed by controlling the rate at which the reaction occurs. The simplest method would be to limit the rate at which the reactants are mixed together. This can also be addressed by noting that the target temperature could be (say) 40 degrees fahrenheit, so excursions up to ~100 degrees fahrenheit during the heating process would be harmless. Finally, it would be possible to surround the heating pellet with a sphere that was free of tissue that might be damaged (e.g., surround the pellet with a sphere of ice containing salts). 3) Tissue stability (cracking, etc) during the heating process might be of concern. This can be addressed by insuring that the thermal coefficient of expansion of the material is small (by, for example, varying the structure of the water between amorphous and crystalline on a sub-micron scale, or otherwise controlling the details of the molecular structure); increasing the strength of the material (by, for example, embedding long protein polymers to increase strength); and by insuring that heating is so rapid that there is insufficient time for any serious damage to occur. This latter forestalls concerns of recrystallization damage which might occur during heating. 4) Leaving heating pellets in place is unaesthetic. Various methods of removing the pellets are feasible. At the cost of increasing the heating time, pellets could be confined to the circulatory system (the distance from any cell to a capillary is ~40 microns). They would then be washed away when circulation resumed. If pellets are designed to be suitably benign, they could dissolve and be washed away (2H2 + O2 is particularly attractive here). For hard pellets, exit tubes could be left in place which would permit the pellets to be ejected. The tubes would themselves be degradable, and would dissolve harmlessly. As the basic physics of the situation are well understood, others might wish to make proposals. Finding a technically simple, aesthetically appealing proposal for rapid heating would seem to be useful, as this question has arisen before and will no doubt arise again. The best proposal could be put on the web, and in the future when this question arises we could simply point to this web page. Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=4741